1. Field of the Invention
The present invention relates to a method and apparatus for generating exposure data which is used to expose a design pattern of a semiconductor integrated circuit on an exposure medium.
2. Description of the Related Art
Larger scale and higher integration have been demanded for recent semiconductor integrated circuits (LSIs), and the amount of exposure data necessary to prepare such an LSI is increasing accordingly. The increased amount of exposure data results in longer exposure time and eventually in longer LSI manufacturing time. There is therefore a demand for the reduction of the amount of exposure data.
FIG. 22 is a schematic structural diagram of a variable rectangular electron beam (EB) exposure apparatus. The EB exposure apparatus 10 has first and second plates 11 and 12 in which rectangular windows 13 and 14 with predetermined areas are respectively formed. The EB exposure apparatus 10 controls an electromagnetic deflector 15 for plate alignment (first electromagnetic deflector) to change the overlapping area of a beam formed by the first plate 11 with the rectangular window 14 of the second plate 12, thereby controlling the cross-sectional shape of the beam exiting the rectangular window 14, or the exposure pattern. The exposure apparatus 10 controls a positioning electromagnetic deflector (second electromagnetic deflector) 16 and a patterning electromagnetic deflector (third electromagnetic deflector) 17 to deflect the transmitted beam, and it moves a stage 18 in the X and Y axial directions to expose a desired pattern on a semiconductor wafer 19 mounted on the stage 18.
The first to third electromagnetic deflectors 15 to 17 and the stage 18 are controlled based on exposure data prepared from design data (pattern data) of a semiconductor chip to be drawn on the semiconductor wafer 19. For example, a semiconductor chip 20 shown in FIG. 23 is formed on the semiconductor wafer 19 in a matrix form. The semiconductor chip 20 is divided into a plurality of fields 21, each of which is further separated into a plurality of subfields 22.
The first electromagnetic deflector 15 is controlled based on the size of a pattern for exposing the subfield 22, so that the beam that passes through the rectangular window 14 is controlled to a cross-sectional shape corresponding to the size of the pattern. The second and third electromagnetic deflectors 16 and 17 and the stage 18 are controlled on the basis of the position of an occasionally drawn pattern. For instance, one field 21 is selected by the stage 18 and one subfield 22 is selected by the second electromagnetic deflector 16. Then, a pattern is exposed onto the selected subfield 22 by the third electromagnetic deflector 17.
Exposure pattern data of the semiconductor chip 20 is generated by an unillustrated exposure data generating apparatus and is supplied to the aforementioned EB exposure apparatus 10. The conventional exposure data generating apparatus extracts pattern data, which repeatedly appears in the exposure pattern data of the semiconductor chip 20, by matrix recognition and prepares exposure data of a matrix form. Further, the conventional exposure data generating apparatus forms exposure data into a hierarchical structure like design data, extracts repeatedly appearing exposure pattern data as a group of exposure pattern data and determines the layout position of that data group to reduce the amount of exposure data. The greater the types of pattern data to be extracted becomes, the less the total amount of necessary exposure data becomes.
A group of exposure pattern data to be extracted includes repeatedly appearing pattern data such as common portions like memory cells. Since a group of exposure pattern data consisting of memory cells is small in area, the number of layouts and the number of exposures of that pattern data become large, and the overall amount of exposure data is thus large.
According to many exposure apparatuses, the electron beam is moved to a predetermined position by various deflections. In the EB exposure apparatus 10 as shown in FIG. 22, for example, the electron beam formed by the first and second plates 11 and 12 is moved to a predetermined position on the semiconductor wafer 19 by the deflection caused by the second and third electromagnetic deflectors 16 and 17 and by the stage 18.
If the amount of layout data indicating the layout positions of a group of exposure pattern data is large, the electron beam cannot be moved to the desired position by the second and third electromagnetic deflectors 16 and 17 alone. To overcome this problem, the relative position of the beam to the wafer 19 is determined by controlling the stage 18. It takes longer time to move the wafer 19 by the stage 18 than to move the beam by the second and third electromagnetic deflectors 16 and 17. Thus, use of the stage for beam positioning increases the control time for the entire apparatus, which increases the overall exposure time of the semiconductor wafer 19.
Further, at the time of executing a process for positioning the beam at a target point by deflection, a positioning error may occur depending on the mechanical precision of the stage. The greater the number of times the beam is positioned, the higher the rate of occurrence of the positioning error becomes, reducing the exposure precision of the whole chip. In this respect, it is desirable to acquire repeating units or repeating exposure data that occupies a large area. However, large areas usually include repeatless patterns, which interfere with matrix recognition. Furthermore, with large areas the amount of data to be extracted increases, thus increasing the extraction time.